Solid ink or phase change ink printers conventionally receive ink in a solid form, which in some printers is referred to as solid ink sticks and in other printers, solid ink pastilles are used. The solid ink forms are typically inserted through an insertion opening of an ink loader for the printer and are moved by a feed mechanism and/or gravity toward a heater plate. The heater plate melts the solid ink impinging on the plate into a liquid that is delivered to a printhead assembly for jetting onto a recording medium. In the direct printing architecture, the recording medium is typically paper, while for an offset printing architecture, the ink is printed onto a liquid layer supported by an intermediate imaging member, such as a metal drum or belt.
A printhead assembly of a phase change ink printer typically includes one or more printheads each having a plurality of inkjets from which drops of melted solid ink are ejected towards the recording medium. The inkjets of a printhead receive the melted ink from an ink supply chamber, or manifold, in the printhead which, in turn, receives ink from a source, such as a melted ink reservoir or an ink cartridge. Each inkjet includes a pressure chamber that is fluidly connected to the manifold to receive ink The pressure chamber is aligned with an actuator and a diaphragm is disposed between the actuator and the pressure chamber. The pressure chamber is also fluidly connected through a channel to an aperture in an aperture plate. During printing, firing signals activate the actuators, which expand and distend the diaphragm into the pressure chamber. This action propels ink from the pressure chamber through the channel to an aperture where a drop of ink is expelled onto the recording medium. By selectively activating the actuators of the inkjets to eject drops as the recording medium and/or printhead assembly are moved relative to each other, the drops can be precisely deposited on the media to form particular text and graphic images.
One difficulty faced by fluid inkjet systems is partially or completely blocked inkjets. Partially or completely blocked inkjets may be caused by a number of factors including contamination from dust or paper fibers, dried ink, etc. In addition, when the solid ink printer is turned off, the ink that remains in the printhead can freeze. When the printer is turned back on and warms up, the ink melts and air that was once in solution in the ink emerges to form air bubbles or air pockets. This air may partially or completely block the fluid path through one or more inkjets and cause missing, undersized or misdirected ink drops on the recording media.
Some partially or completely blocked inkjets may be recovered by performing printhead maintenance. Printhead maintenance generally includes pressurizing the space in a printhead to force ink through the ink pathways of a printhead. This forced ink flow clears contaminants, air bubbles, dried ink, etc. from the fluid paths in the printhead and some of the ink is expelled from the apertures onto the area of the aperture plate surrounding the apertures. A wiper is then swiped across the aperture plate to remove the ink from the aperture plate of the printhead. While the printhead maintenance may restore some inkjet ejectors, the purging action expels some ink that does not contribute to the recovery of weak or missing jets.
Printheads may be arranged in rows within a printer to print across a width of the recording medium. Previously known purging methods allow individual printheads to be selected for maintenance so printheads in which no inoperative or malfunctioning inkjets were detected can skip a printhead maintenance procedure. In this manner, ink can be better preserved. The printers using these purging methods, however, require each printhead to have a separate wiper. A separate wiper is necessary for each printhead because wiping inkjets that do not have ink present on the front face of the printhead may damage the inkjets. Apparently, the presence of the ink helps reduce the friction caused by wiping the face plate and this friction is thought to be the cause of the inkjet damage that may occur during wiping. Improving printhead maintenance procedures and systems to enable the use of fewer wipers without subjecting each printhead to a purging operation is a desirable goal.